Glaucoma Drainage Devices

Jun 8, 2015

Glaucoma Drainage Devices. Part 4 of 12 of “What’s New In Glaucoma Surgery” Presentation, a continuing education course for Optometrists presented by Patient-Focused Ophthalmologist, Dr. David Richardson on May 20, 2015.

Glaucoma Drainage Devices

So, glaucoma drainage devices… Many people don’t know glaucoma drainage devices actually appeared on-scene around the same time as Trabeculectomy did. They also have a very interesting history and I enjoy the kind of interesting stories of history, which is funny because when I was a student I hated history. It was dry and dusty it probably because that’s the way it was taught. But now we’ve discovered through the wonderful PBS documentaries that history can be pretty interesting. And it is. And it’s true in our own fields.

Glaucoma drainage devices also have an interesting history. The first drainage devices out there were called, “Setons”. Setons are basically just a filament. Something that you put in a position to keep a hole open so they’re not tubes. They don’t have any lumen inside them they’re just a placeholder and some of the earliest Setons that were described in the literature include: horsehair, glass, and then every precious metal you can think of. None of them none of them really works. So they’ll basically scarred-downed or became infected or the Setons basically were extruded. So glaucoma drainage devices were the next step and what really made glaucoma drainage devices work is that instead of just putting a tube in the eye, letting fluid flow from anterior chamber underneath the subconjuctival. The key is that there’s a plate. So essentially a reservoir forms. The fluid moves through the tube unto the plate and then out usually through subconjuctival space. Into the drainage vessels.

Now the problem with glaucoma drainage devices is that it can be difficult, just as Trabeculectomy, to achieve that right balance because the tubes that we currently use with glaucoma drainage devices are all so – the lumens are so large that there’s really no significant restriction to flow. They just put them in and let the fluid go. Everyone’s going to be hypotonous. And indeed that’s one of the issues with glaucoma drainage devices which is why with Baerveldt’s we have to tie it off for a period of time and basically sit there and wait. Well it opens up, which means of course that the pressures too high during that time or with the Ahmed there’s actually a valve which does restrict the flow a bit in the lab it works beautifully in terms of flow restriction but in humans for some reason you can still get hypotony. So early on after surgery you can still get too much flow even than though there’s a valve over a flow restrictor that should in theory keep it from going to low and then of course there’s the issue that a month or so out most patients who have glaucoma drainage devices end up with what we call a hypertensive phase. Well the body is going to heal around this and as it does so you end up with more restrictions to the outflow and you can actually end up with a hypertensive face before the healing process is completed. And then of course it depends on how the body heals long-term. If somebody develops a very thick wall a fibrous tissue around these devices you’re not going to end up with good long-term results. And then there are all the issues and just an implant. This is true for any implant you put in the eye or anywhere else in the body: the implants can move! Implants can get infected and implants that get infected have to be removed. Scarring can result in things like restriction of the tissue around these implants and at least in the case of the Baerveldt which sits underneath the extra ocular muscles you can end up with double vision.

So these are the basic glaucoma treatments that we’ve had available for decades. And for those who have severe glaucoma and there’s nothing else that we can really offer, when we’re facing loss of vision it’s been a trade-off we’ve been willing to accept. We’ve been willing to accept it. I’m not so sure that our patients have been so willing. But in the past patients were also much more likely to just do what their doctors told them. That’s no longer the case and I personally am getting more and more patients when told that they need Trabeculectomy or glaucoma drainage device just say, ‘no I won’t have it. I’d rather go blind.” And I just had somebody in my office the other day. It was a little stressful for me because she was adamant she didn’t want Trabeculectomy and she and her son were arguing in front of me. He was telling her she was going to go blind eye and I was agreeing she would if she didn’t have her pressure lowered. Fortunately she did have other options but prior to coming to see me the only option she had been given was Trabeculectomy and her surgeon was not willing to even consider any other options.

So we have to be willing now to accept that we need to work with our patients and they do have the right to determine what happens to their eye just like they have that right to determine what happens to the any other part of their body. And we may not agree with their decision. It’s good now that we have a number of these newer technologies and procedures that were going to be talking about. So this is just the yet couple of the risks of glaucoma drainage device. Here’s a tube it’s tearing through the cornea. This here is a suprachoroidal hemorrhage this can happen after any glaucoma surgery but it’s more likely after Trabeculectomy or glaucoma drainage devices because there’s the potential that your pressure could end up too low. If your pressure’s too low you can actually end up with the choroidal vessels leaking or bursting. And this is a blinding condition (the suprachoroidal hemorrhage). Let’s move on to some of the newer technologies.